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    <title>Document</title>
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    <!-- 求出1-1/2+1/3-1/4…..1/100的和 var i=1; 100是参数 -->
    <script>
        function fn(a) {
            var sum = 0;
            for (var i = 1; i <= a; i++) {
                if (i % 2 === 0) {
                    sum -= 1 / i;
                } else {
                    sum += 1 / i;
                }
            }
            console.log(sum);
        }
        fn(100);
    </script>
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